8. The therapeutic effects of cannabinoids

8.5 Cannabinoids as anti-asthmatic agents

Smoked cannabis, and to a lesser extent oral THC, have an acute bronchodilatory effect in both normal persons and persons with asthma (Tashkin et al, 1975; Tashkin et al, 1976). Tashkin et al (1975), for example, compared the bronchodilator effect of smoked cannabis with that of a standard clinical dose of the bronchodilator isoproterenol in relieving experimentally induced asthma in asthmatic patients. They found that smoking a 2 per cent-THC cannabis cigarette produced a bronchodilator nearly equivalent to that of a clinical dose of isoproterenol.

Despite this early suggestion of a therapeutic effect in asthma, cannabinoids have not been used therapeutically, nor have they been extensively investigated as anti-asthmatic agents other than by Tashkin and his colleagues (Tashkin, 1993). A major obstacle to therapeutic use has been the route of administration. Oral THC produces a smaller bronchodilator effect after a substantial delay, and when used as an inhalant produces irritation and reflex bronchoconstriction. Hence, smoking marijuana has been the most dependable way of delivering a clinically effective dose of THC. There is an understandable concern among clinical researchers that smoking is an unsuitable mode of administering any drug, and an especially inappropriate way to administer a drug to patients with asthma, because it would inevitably involve the delivery of other noxious chemicals that would nullify its therapeutic value in the short term, and carry an increased risk of other respiratory disease and possibly cancer in the long term (Tashkin, 1993). The unwanted psychotropic effects from marijuana smoking have also been a barrier to its use as an anti-asthmatic drug. Some investigators (e.g. Graham, 1986) have nonetheless argued that the suitability of THC as a spray should be further investigated because of the possible hazards of the chronic use of the more widely-used beta-blocker antagonists. The recent discovery of the cannabinoid receptor and ligand may prompt a re-examination of this question.